U.S. patent application number 12/822619 was filed with the patent office on 2010-12-30 for mold for injection molding and manufacturing method of injection-molded product.
This patent application is currently assigned to SUZUKI MOTOR CORPORATION. Invention is credited to Hiroaki Nagashima.
Application Number | 20100327491 12/822619 |
Document ID | / |
Family ID | 43307947 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100327491 |
Kind Code |
A1 |
Nagashima; Hiroaki |
December 30, 2010 |
MOLD FOR INJECTION MOLDING AND MANUFACTURING METHOD OF
INJECTION-MOLDED PRODUCT
Abstract
A provisional rib portion is formed in a connected manner at a
predetermined portion of a cavity to correspond to a provisional
rib which is formed to project from a portion, of an
injection-molded product, not serving as a design surface, and
resin is injected for molding to the provisional rib portion via a
gate. An end portion of the design surface of the injection-molded
product is set on a parting line, and the provisional rib portion
is formed in a connected manner, on a cavity surface along the
parting line, by being sided to an inner side from the design
surface, and a part or all on the design surface side of a
connecting portion at which the provisional rib portion and the
cavity are connected is formed in a curved shape.
Inventors: |
Nagashima; Hiroaki;
(Shizuoka, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SUZUKI MOTOR CORPORATION
Shizuoka
JP
|
Family ID: |
43307947 |
Appl. No.: |
12/822619 |
Filed: |
June 24, 2010 |
Current U.S.
Class: |
264/328.1 ;
425/567 |
Current CPC
Class: |
B29C 45/2708 20130101;
B29C 2045/0036 20130101; B29C 2045/0027 20130101; B29C 45/0025
20130101; B29C 2045/0034 20130101 |
Class at
Publication: |
264/328.1 ;
425/567 |
International
Class: |
B29C 45/18 20060101
B29C045/18; B29C 45/27 20060101 B29C045/27 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2009 |
JP |
2009-151564 |
Claims
1. A mold for injection molding, comprising a provisional rib
portion formed in a connected manner at a predetermined portion of
a cavity to correspond to a provisional rib which is formed to
project from a portion, of an injection-molded product, not serving
as a design surface, and resin is injected for molding to said
provisional rib portion via a gate, wherein: an end portion of the
design surface of the injection-molded product is set on a parting
line, and said provisional rib portion is formed in a connected
manner, on a cavity surface along the parting line, by being sided
to an inner side from the design surface; and a part or all on at
least the design surface side of a connecting portion at which said
provisional rib portion and the cavity are connected is formed in a
curved shape.
2. The mold for injection molding according to claim 1, wherein
said provisional rib portion is formed by being sided to the inner
side from the design surface by less than 1.0 mm.
3. The mold for injection molding according to claim 1, wherein
arc-shaped corner portions formed to satisfy a condition of
R.gtoreq.0.5 are provided to form the curved shape.
4. The mold for injection molding according to claim 2, wherein
arc-shaped corner portions formed to satisfy a condition of
R.gtoreq.0.5 are provided to form the curved shape.
5. The mold for injection molding according to claim 1, wherein the
injection-molded product has a side wall including the design
surface, and a lower end of the side wall is set and the connecting
portion is formed on a cavity surface along the parting line.
6. The mold for injection molding according to claim 2, wherein the
injection-molded product has a side wall including the design
surface, and a lower end of the side wall is set and the connecting
portion is formed on a cavity surface along the parting line.
7. The mold for injection molding according to claim 3, wherein the
injection-molded product has a side wall including the design
surface, and a lower end of the side wall is set and the connecting
portion is formed on a cavity surface along the parting line.
8. The mold for injection molding according to claim 4, wherein the
injection-molded product has a side wall including the design
surface, and a lower end of the side wall is set and the connecting
portion is formed on a cavity surface along the parting line.
9. The mold for injection molding according to claim 1, wherein the
gate is a submarine gate or a nose gate.
10. A manufacturing method of an injection-molded product for
injecting resin for molding to a provisional rib portion via a
gate, the provisional rib portion being formed in a connected
manner at a predetermined portion of a cavity to correspond to a
provisional rib which is formed to project from a portion, of the
injection-molded product, not serving as a design surface, the
method comprising performing injection molding by using a mold for
injection molding having the provisional rib portion formed in a
connected manner, by being sided to an inner side from the design
surface, on a cavity surface along a parting line on which an end
portion of the design surface of the injection-molded product is
set, and a connecting portion at which the provisional rib portion
and the cavity are connected in which a part or all thereof on at
least the design surface side is formed in a curved shape.
11. The manufacturing method of the injection-molded product
according to claim 10, wherein the mold for injection molding
having the provisional rib portion that is formed by being sided to
the inner side from the design surface by less than 1.0 mm is
used.
12. The manufacturing method of the injection-molded product
according to claim 10, wherein the mold for injection molding in
which arc-shaped corner portions formed to satisfy a condition of
R.gtoreq.0.5 are provided to form the curved shape is used.
13. The manufacturing method of the injection-molded product
according to claim 11, wherein the mold for injection molding in
which arc-shaped corner portions formed to satisfy a condition of
R.gtoreq.0.5 are provided to form the curved shape is used.
14. The manufacturing method of the injection-molded product
according to claim 10, wherein the injection-molded product has a
side wall including the design surface, and the mold for injection
molding having the connecting portion formed on a cavity surface
along the parting line on which a lower end of the side wall is set
is used.
15. The manufacturing method of the injection-molded product
according to claim 11, wherein the injection-molded product has a
side wall including the design surface, and the mold for injection
molding having the connecting portion formed on a cavity surface
along the parting line on which a lower end of the side wall is set
is used.
16. The manufacturing method of the injection-molded product
according to claim 12, wherein the injection-molded product has a
side wall including the design surface, and the mold for injection
molding having the connecting portion formed on a cavity surface
along the parting line on which a lower end of the side wall is set
is used.
17. The manufacturing method of the injection-molded product
according to claim 13, wherein the injection-molded product has a
side wall including the design surface, and the mold for injection
molding having the connecting portion formed on a cavity surface
along the parting line on which a lower end of the side wall is set
is used.
18. The manufacturing method of the injection-molded product
according to claim 10, wherein the mold for injection molding
having the gate that is a submarine gate or a nose gate is used.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2009-151564,
filed on Jun. 25, 2009, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a mold for injection
molding and a manufacturing method of an injection-molded product,
and particularly relates to a technique for improving a quality of
outer appearance of the injection-molded product.
[0004] 2. Description of the Related Art
[0005] In recent years, in an interior of automobile, for instance,
resin parts painted in a silver metallic color have been
increasingly adopted for improving design. However, in painting
process, volatile organic compounds (hereinafter, referred to as
VOC) contained in the paint may be emitted into the atmosphere, and
further, the VOC ascribable to the paint may be generated in a
vehicle interior. Accordingly, it is desired to mold colored resins
into which coloring agent and luminous agent are previously
kneaded, instead of performing painting.
[0006] So far, there have been a large number of examples where
unpainted interior parts of automobile in a solid color such as
black color and white color are actually used. However, regarding
the unpainted interior parts in silver metallic color, since the
parts sometimes bear, on outer surfaces thereof, black-streaks
called weld lines due to a luminous material such as aluminum
powder or mica powder contained in resin, and thus there are very
few cases where the interior parts are actually commercialized.
[0007] Although it is also desired not to perform painting in
silver metallic color on an audio volume knob, for instance, it was
difficult to be realized since the weld lines are sometimes
generated in the vicinity of a gate. This is due to a gate
structure when the volume knob is injection-molded.
[0008] In FIGS. 7, FIG. 7A is a view showing a cross section of a
mold having an overlap gate, and FIG. 7B is a view showing a volume
knob molded by the mold having the overlap gate.
[0009] The mold having the overlap gate as shown in FIG. 7A is
composed of a die 61 (movable side or fixed side) and the other die
62 (fixed side or movable side), and a cavity 64 is formed by
closing these dies along a parting line 63. Further, molten resin
is injected to fill the cavity 64 from a runner 65 via an overlap
gate 66, to thereby perform molding.
[0010] The volume knob being a molded product shown in FIG. 7B has
a box shape or a bottomed cylindrical shape, and in order to
realize simplicity of machining of dies and not to leave a trace of
gate-cut on a design surface, it is common that the resin is filled
into the cavity 64 via the overlap gate 66 as shown in FIG. 7A.
However, if the overlap gate 66 is employed, weld lines (WL) are
generated from a corner portion of an abutting surface at which a
gate portion 67 formed of the overlap gate 66 and a molded product
main body 68 abut, as shown in an enlarged view in FIG. 7B. This is
because the flow of the injected resin is branched at a corner
portion of a connecting portion at which the overlap gate 66 and
the cavity 64 are connected (arrows in FIG. 7B), the resin collides
at a design surface (outer surface) of the molded product main body
68, and orientation of the luminous material such as aluminum
powder added to the resin occurs.
[0011] Here, Patent Document 1 (Japanese Patent No. 4120701)
discloses that, by rounding a corner portion of a side gate, it is
possible to prevent the generation of weld lines starting from the
corner portion.
[0012] [Patent Document 1] Japanese Patent No.
[0013] [Patent Document 2] Japanese Laid-open Patent Publication
No. 08-41284
[0014] [Patent Document 3] Japanese Patent No. 3571403
[0015] However, in a structure disclosed in Patent Document 1,
since the side gate is disposed at a position corresponding to a
side surface portion of a molded product, a product such as a
volume knob bears a trace of gate-cut on its design surface, and
thus it cannot be used as a marketable product, although the
generation of weld lines can be prevented. Further, if the overlap
gate is employed, a corner portion of a connecting portion at which
the overlap gate is connected to a cavity cannot be rounded due to
the presence of undercut because of its structural reason, and thus
the problem of the weld lines cannot be solved.
[0016] As a measure other than the one relying on the gate
structure, there is a measure relying on a material. For example,
in Patent Document 2 (Japanese Patent Application Laid-open No. Hei
8-41284), the generation of weld lines is reduced by selecting the
shape or grain size of a luminous material added to a resin
material. Further, in Patent Document 3 (Japanese Patent No.
3571403), the generation of weld lines is reduced by selecting a
grain size and an addition amount of a luminous material and by
adding titanium oxide, zinc oxide or antimony oxide which is called
a weld eraser.
[0017] However, since the shape, grain size and addition amount of
the luminous material are restricted in the techniques disclosed in
Patent Document 2 and Patent Document 3, textures such as shiny
texture and metallic texture are limitedly produced, resulting in
that there are a lot of cases where a highly metallic color tone as
an alternative to the texture produced by painting cannot be
obtained. Further, these techniques are not capable of completely
preventing the generation of weld lines, and cost is increased
depending on a blending condition, which is a problem.
SUMMARY OF THE INVENTION
[0018] The present invention has been made in consideration of such
circumstances, and an object thereof is to provide a mold for
injection molding and a manufacturing method of an injection-molded
product capable of providing various types of injection-molded
products with high commercial value by improving a quality of outer
appearance of the injection-molded product with no restriction on a
molding material.
[0019] A mold for injection molding of the present invention being
a mold for injection molding including a provisional rib portion
formed in a connected manner at a predetermined portion of a cavity
to correspond to a provisional rib which is formed to project from
a portion, of an injection-molded product, not serving as a design
surface, and resin is injected for molding to the provisional rib
portion via a gate, in which an end portion of the design surface
of the injection-molded product is set on a parting line, and the
provisional rib portion is formed in a connected manner, on a
cavity surface along the parting line, by being sided to an inner
side from the design surface, and a part or all on at least the
design surface side of a connecting portion at which the
provisional rib portion and the cavity are connected is formed in a
curved shape.
[0020] Further, a manufacturing method of an injection-molded
product of the present invention being a manufacturing method of an
injection-molded product for injecting resin for molding to a
provisional rib portion via a gate, the provisional rib portion
being formed in a connected manner at a predetermined portion of a
cavity to correspond to a provisional rib which is formed to
project from a portion, of the injection-molded product, not
serving as a design surface, the method including performing
injection molding by using a mold for injection molding having the
provisional rib portion formed in a connected manner, by being
sided to an inner side from the design surface, on a cavity surface
along a parting line on which an end portion of the design surface
of the injection-molded product is set, and a connecting portion at
which the provisional rib portion and the cavity are connected in
which a part or all thereof on at least the design surface side is
formed in a curved shape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a view showing a mold for injection molding
according to an embodiment of the present invention;
[0022] FIGS. 2A and 2B are views showing a molded product molded by
the mold for injection molding according to the embodiment of the
present invention;
[0023] FIG. 3 is a view showing a provisional rib portion formed on
the mold for injection molding according to the embodiment of the
present invention;
[0024] FIGS. 4A and 4B are views for explaining a size condition
according to examples of the present invention;
[0025] FIG. 5 is a view for explaining weld lines and a flow mark
generated on a molded product;
[0026] FIGS. 6A, 6B and 6C are views showing modified examples of a
connecting portion of a provisional rib portion according to the
present invention; and
[0027] FIGS. 7A and 7B are views showing a mold that employs an
overlap gate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Hereinafter, a preferred embodiment of a mold for injection
molding and a manufacturing method of an injection-molded product
according to the present invention will be described. FIG. 1 is a
view showing a mold for injection molding (hereinafter, referred to
as mold) 10 according to the present embodiment, and FIGS. 2A and
2B are views showing a molded product 100 molded (manufactured) by
the mold 10.
[0029] At first, a schematic structure of the mold 10 according to
the present embodiment will be described. As shown in FIG. 1, the
mold 10 is composed of a die (movable side or fixed side) and a die
12 (fixed side or movable side), and a cavity 14 is formed by
closing these dies along a parting line 13.
[0030] A runner 15 is formed along the parting line 13 by being
separated from a design surface 100a (one-dot chain line in FIG. 1)
of the molded product 100 shown in FIG. 2 formed by the cavity 14,
and through which molten resin from a not-shown sprue flows into
the cavity 14. More specifically, the molten resin that flows into
the cavity 14 through the runner 15 is injected to fill the cavity
14 by passing through a submarine gate 16 and a provisional rib
portion 17. As above, the mold 10 has a structure of die employing
a so-called submarine gate, so that there is an undercut 12a in the
die 12.
[0031] In the present embodiment, a product such as an audio volume
knob is assumed as a molded product 100 molded by the mold 10, and
a molded product 100 having a relatively thin side wall 100b
indicated by a dotted line in FIG. 1 and having a box shape or a
bottomed cylindrical shape is molded (refer also to FIGS. 2). An
outer surface of the molded product 100 is set as a design surface
100a, and an outer surface of the side wall 100b is also included
in a part of the design surface 100a. In this case, the design
surface 100a is formed by a cavity surface 14a of the cavity 14
having a substantially U-shape in cross section.
[0032] Further, in the molded product 100, a provisional rib 101
(enlarged view in FIG. 1) is formed to project from a portion not
serving as the design surface 100a, and to correspond to the
provisional rib 101, the provisional rib portion 17 is formed in a
connected manner at a predetermined portion of the cavity 14 of the
mold 10. The provisional rib portion 17 is formed to prevent the
generation of weld lines, and is communicated with the runner 15
via the submarine gate 16 to inject the molten resin to fill the
cavity 14 (in other words, the provisional rib portion 17 also
serves as a gate). Note that the provisional rib portion 17 is
formed on the die 12 through cutting or the like, and the
provisional rib 101 formed by the provisional rib portion 17 is cut
after the molding.
[0033] The provisional rib portion 17 will be specifically
described. In the present embodiment, an end portion P of the
design surface 100a of the molded product 100 is set on the parting
line 13, and a surface of a lower end of the side wall 100b of the
molded product 100 including the end portion P of the design
surface 100a is formed by a cavity surface 14b which is flat along
the parting line 13 (enlarged view in FIG. 1). The provisional rib
portion 17 is formed in a connected manner at a predetermined
position of the cavity surface 14b sided to an inner side from the
end portion P of the design surface 100a, namely, at a
predetermined position of the cavity surface 14b separated from the
end portion P of the design surface 100a by a distance (clearance)
a. Note that the clearance a indicates a distance from the design
surface 100a to an end portion or an end side of the provisional
rib portion 17 that points to the design surface 100a side.
[0034] As described above, the mold 10 employs a structure such
that the molten resin is injected to fill the provisional rib
portion 17 via the submarine gate 16 so that any of the sides of
the provisional rib 101 does not overlap with the end portion P of
the design surface 100a. Further, with such a structure, weld
lines, starting from a corner portion of a connecting portion at
which a gate of resin and a cavity are connected, are prevented
from being generated on a design surface of a molded product.
[0035] Here, the mold 10 in the present embodiment is assumed to
mold a relatively thin-walled molded product 100 having a box
shape, a bottomed cylindrical shape or the like. In this case, even
if the provisional rib portion 17 is provided, due to a restriction
on the size condition such as a thickness of the side wall 100b of
the molded product 100 and a thickness of the provisional rib
portion 17, the clearance a (refer to enlarged view in FIG. 1)
being a distance between the provisional rib portion 17 and the
design surface 100a sometimes cannot be sufficiently secured, and
further, an area of a connecting part at which the provisional rib
portion 17 and the cavity 14 are connected (hereinafter, referred
to as connecting portion) sometimes cannot be sufficiently secured.
If the clearance a cannot be sufficiently secured, even when the
provisional rib portion 17 is provided, a weld line (WL) starting
from the provisional rib portion 17 may be generated on the design
surface 100a, and further, if the area of the connecting portion
between the provisional rib portion 17 and the cavity 14 cannot be
sufficiently secured, an outer appearance such as flow mark (FM)
and jetting may appear on the design surface 100a. Note that the
flow mark and the jetting are easily generated as the area of gate
(connecting portion between the provisional rib portion 17 and the
cavity 14, in this case) becomes smaller, and are one of defects in
outer appearance.
[0036] However, when the molded product 100 has a thin wall, there
are generated contradictory relations such that if the clearance a
of the provisional rib portion 17 is tried to be sufficiently
secured, the area of the connecting portion at which the
provisional rib portion 17 and the cavity 14 are connected cannot
be sufficiently secured, and if the area of the connecting portion
is tried to be sufficiently secured, the clearance a cannot be
sufficiently secured. Further, when the both relations cannot be
satisfied, the quality of outer appearance of the molded product
100 cannot be assured, and a necessity of applying painting and the
like is generated, which may lead to an increase in cost.
[0037] Therefore, in the mold 10 according to the present
invention, a part or a front portion on at least the design surface
100a side of the connecting portion at which the provisional rib
portion 17 and the cavity 14 are connected is formed in a curved
shape. In this embodiment, arc-shaped corner portions (namely,
rounded corner portions) are provided to form the curved shape, and
by rounding corner portions on at least the design surface 100a
side of the connecting portion, the quality of outer appearance is
improved even when the clearance a and the area of the connecting
portion cannot be sufficiently secured. Note that as the curved
shape, not only the one formed by the arc-shaped corner portions
but also an elliptical shape or a circular shape and the like can
be selected, as will be described later.
[0038] In FIGS. 2, FIG. 2A shows a front view of the molded product
100, and FIG. 2B shows a bottom view. Further, FIG. 3 is a
perspective view showing the cavity 14 and the provisional rib
portion 17.
[0039] Here, it is set that the connecting portion between the
provisional rib portion 17 and the cavity 14 is a boundary area
between the both along the parting line 13 (strictly, boundary
surface; parting surface). As also shown in FIG. 1 and the like,
the provisional rib portion 17 has a predetermined length in a
direction in which the mold is opened/closed (longitudinal
direction in FIG. 1), and corner portions in a longitudinal
direction thereof are not rounded, namely, only the corner portions
at the aforementioned boundary area are rounded to form the
connecting portion.
[0040] Specifically, in the molded product 100, the corner portions
positioned on the design surface 100a side of the provisional rib
101 are rounded, namely, formed in an arc shape (101b), as shown in
FIG. 2B. In accordance with this, in the provisional rib portion
17, the corner portions on the design surface 100a side of the
connecting portion 17a being a connecting part between the
provisional rib portion 17 and the cavity 14 are rounded (R
portions 17b), as shown in FIG. 3.
[0041] As described above, in the mold 10, by forming the R
portions 17b by rounding the corner portions on the design surface
100a side of the connecting portion 17a between the provisional rib
portion 17 and the cavity 14 so that they are formed in a curved
shape, even when the clearance a cannot be sufficiently secured due
to the wall thickness of the molded product 100, the quality of
outer appearance is assured. Specifically, by forming the R
portions 17b to make the flow of the molding material smooth, the
generation of weld lines is prevented, and the quality of outer
appearance of the molded product 100 is assured.
[0042] As described above, in the mold 10 according to the
embodiment of the present invention, the R portions 17b are formed
by rounding the corner portions on the design surface 100a side of
the connecting portion 17a between the provisional rib portion 17
and the cavity 14 so that they are formed in a curved shape. As a
result of this, even when the clearance a cannot be sufficiently
secured due to the wall thickness of the molded product 100, the
generation of weld lines is surely prevented by making the flow of
the molding material smooth with the use of the R portions 17b.
[0043] Further, the mold 10 according to the present embodiment can
be effectively utilized particularly when the area of the
connecting portion 17a between the provisional rib portion 17 and
the cavity 14 cannot be sufficiently secured if a thickness b of
the provisional rib portion 17 is reduced to secure the clearance a
due to the shape of the molded product 100. Specifically, by
forming the R portions 17b, the generation of weld lines can be
prevented without reducing the thickness of the provisional rib
portion 17 to secure the clearance a, so that the area at the
connecting portion 17a can be sufficiently secured, which results
in preventing the generation of flow mark and jetting, in addition
to the weld lines.
[0044] Further, in the mold 10 according to the present embodiment,
since the molding material filled in the submarine gate 16 is
automatically cut when the mold is opened, only one cutting process
of the provisional rib 101 is necessary, so that when compared with
a case in which the overlap gate is employed, there is no increase
in the number of cutting processes. Accordingly, cost reduction can
be practically realized while improving the quality of outer
appearance.
[0045] Further, the mold 10 according to the present embodiment
realizes the assurance of the quality of outer appearance from the
structural aspect, so that it is applicable to a case where a resin
material containing a luminous material such as aluminum powder or
mica powder and thus having high metallic texture, which has been
difficult to be mass-produced, is used, and there is no restriction
on the shape, grain size and addition amount of the luminous
material, which makes it possible to provide various types of
molded products with high commercial value. Further, with the use
of the mold 10 according to the present embodiment, since the
necessity of painting can be eliminated, a cost-down effect can be
obtained, and a significant contribution to the environment is made
because of the reduction in VOC.
Examples
[0046] Hereinafter, examples of the present invention will be
described together with comparative examples. In the present
examples and the comparative examples, audio volume knobs each
having a side wall whose wall thickness (plate thickness) is 2.0 mm
and having a box shape or a bottomed cylindrical shape are molded.
In the examples, the mold according to the present invention in
which the provisional rib portion 17 is provided and the corner
portions of the connecting portion 17a at which the provisional rib
portion 17 and the cavity 14 for forming the volume knob are
connected are rounded, is used. Meanwhile, in the comparative
examples, a mold having a submarine gate in which a provisional rib
portion is provided and corner portions of a connecting portion
between the provisional rib portion and a cavity are not formed in
a curved shape, namely, the connecting portion is formed in a
rectangular shape, is used.
[0047] Further, as a molding material in the present examples and
the comparative examples, AES resin is selected, and the resin to
which 2.0 weight percent of aluminum powder having an average grain
size of 5 .mu.m is added, is used. Note that in general, aluminum
powder has an average grain size of 5 .mu.m to 90 .mu.m, in which
there is a characteristic such that as the grain size is smaller, a
high metallic texture can be obtained and a design is improved,
but, an outer appearance such as a weld line and a flow mark is
easily generated.
Comparative Example
[0048] At first, the comparative examples will be explained. As
described above, in the comparative examples, there is used the
mold having the submarine gate in which the provisional rib portion
is provided and the corner portions of the connecting portion
between the provisional rib portion and the cavity are not formed
in a curved shape, namely, the connecting portion is formed in a
rectangular shape. FIG. 4A shows a shape of the provisional rib
portion of the mold according to the comparative examples or a
provisional rib formed on the volume knob. As shown in FIG. 4A, in
the mold according to the comparative examples, the connecting
portion between the provisional rib portion and the cavity has a
rectangular shape. In the comparative examples, the volume knobs
are molded using such a mold by setting a wall thickness t of a
molded product (side wall) to 2.0 mm and a width c of the
provisional rib portion (connecting portion) to 5.0 mm, while
changing a size of the clearance a and a thickness b of the
provisional rib portion (connecting portion), and a state of outer
appearance is observed. Note that in the volume knobs molded here,
the relation of "wall thickness t of molded product=clearance
a+thickness b of provisional rib portion" is satisfied. The
relation of the state of outer appearance with respect to the
respective conditions is shown in Table 1. Note that the reason why
the width c of the provisional rib portion is fixed to 5.0 mm in
this case is to make it possible to perform the gate-cut with no
problem at the time of mass production, and 5.00 mm is set as an
upper limit value.
TABLE-US-00001 TABLE 1 Relation between clearance a and outer
appearance (comparative examples) THICKNESS b OF WIDTH c OF
PROVISIONAL PROVISIONAL CLEARANCE a RIB PORTION RIB PORTION WELD
LINE FLOW MARK 0.2 mm 1.8 mm 5.0 mm GENERATED NOT GENERATED 0.4 mm
1.6 mm 5.0 mm GENERATED GENERATED MORE OR LESS 0.6 mm 1.4 mm 5.0 mm
GENERATED GENERATED 0.8 mm 1.2 mm 5.0 mm GENERATED MORE GENERATED
OR LESS 1.0 mm 1.0 mm 5.0 mm NOT GENERATED GENERATED
[0049] As shown in Table 1, it can be confirmed that when the
clearance a is small (a=0.2 to 0.8 mm), the weld line is generated,
and in order to prevent the generation of weld line, there is a
need to set the clearance a to at least 1.00 mm or more.
[0050] However, it is clarified that when the clearance a is set to
0.4 mm or more, an outer appearance called flow mark (FM, refer to
FIG. 5B) is generated, and meanwhile, when the clearance a is set
to 0.2 mm, although the weld line (FIG. 5A) is generated, no flow
mark is generated. This can be considered because, if the clearance
a is set large, namely, if the thickness of the provisional rib
portion 17 is reduced under the condition where the wall thickness
of the volume knob is thin, the area of the connecting portion
between the provisional rib portion 17 and the cavity is reduced,
and the molding material does not flow smoothly. Specifically, it
is clarified that if considering from the result obtained when the
clearance a is set to 0.2 mm, there is a need to set the area of
the connecting portion to at least 8.00 mm.sup.2 or more,
preferably 9.0 mm.sup.2 or more, in order to prevent the generation
of flow mark. Note that in FIG. 5, a provisional rib formed by the
provisional rib portion is denoted by 101'.
Examples of the Present Invention
[0051] In the comparative examples, to enlarge the area of the
connecting portion between the provisional rib portion and the
cavity can be considered as a measure to prevent the generation of
flow mark, but, if the width c of the provisional rib portion is
enlarged, the gate-cut is difficult to be performed, and thus it is
unrealistic when considering the mass production. Accordingly, in
the examples of the present invention, the area of the connecting
portion 17a of the provisional rib portion 17 is secured to prevent
the generation of flow mark and jetting, and the corner portions of
the connecting portion 17a between the provisional rib portion 17
and the cavity 14 are rounded while considering the problem
regarding the gate-cut. Specifically, although the basic shape of
the connecting portion 17a is a rectangular shape, the provisional
rib portion 17 is machined in the die 12 so that the corner
portions of the rectangular shape on the design surface side of the
volume knob are rounded.
[0052] FIG. 4B shows a shape of the provisional rib portion 17 of
the mold according to the examples or a provisional rib formed on
the volume knob. In the examples, R portions 17b are formed on the
corner portions of the connecting portion 17a in the mold by
setting the clearance a, the thickness b of the provisional rib
portion 17 or the connecting portion 17a and the width c shown in
FIG. 4B to 0.2 mm, 1.8 mm and 5 mm, respectively, while securing
9.00 mm.sup.2 of the area of the connecting portion 17a to prevent
the generation of flow mark. Further, by changing the values of R,
the optimum value is selected. Table 2 shows a relation between the
values of R and the generation of weld lines. Note that in the
volume knob molded here, the relation of "wall thickness t of
molded product=clearance a+thickness b of provisional rib portion
17" is satisfied, which is the same as the comparative examples,
and the reason why the width c of the provisional rib portion 17 is
fixed to 5.0 mm is to make it possible to perform the gate-cut with
no problem at the time of mass production, which is also the same
as the comparative examples.
TABLE-US-00002 TABLE 2 Relation between R and weld line (examples)
R WELD LINE NONE GENERATED 0.3 GENERATED MORE OR LESS 0.5 NOT
GENERATED
[0053] As shown in Table 2, there is obtained a result indicating
that under the size condition of the present examples, it is
possible to prevent the generation of weld lines by setting that
R=0.5. Accordingly, it can be confirmed that even in a situation
where only 0.2 mm of clearance a can be secured, the generation of
weld lines can be prevented by setting that R.gtoreq.0.5.
[0054] Further, since no weld line is generated when the clearance
a is equal to or more than 1.0 mm based on the result of the
comparative examples, it can be considered that when the clearance
a is 0.2 mm or more, the generation of weld lines can be securely
prevented by setting that R.gtoreq.0.5, and the present invention
can be confirmed to be effective in a situation where only the
clearance a of less than 1.00 mm can be set.
[0055] Further, it can be confirmed that in the examples, since the
generation of weld lines is prevented by forming the R portions 17b
while securing 9.00 mm.sup.2 of the area of the connecting portion
17a of the provisional rib portion 17, both the generation of flow
mark and the generation of weld lines can be prevented.
Accordingly, it can be confirmed that the present invention can be
particularly effectively utilized when there is a contradictory
relation between the securement of clearance a and the securement
of area of the connecting portion 17a of the provisional rib
portion 17. In addition, it is possible to eliminate a problem
regarding the gate-cut by setting the width c of the connecting
portion 17a to 5.00 mm when the area of the connecting portion 17a
is set to 9.00 mm.sup.2.
[0056] Although the embodiment and the examples of the present
invention have been described above, the present invention is not
limited to the aforementioned embodiment and examples, and changes
and the like can be made without departing from the scope of the
present invention. For example, the shape and so on of the molded
product 100 are not limited to those in the shown example, and the
present invention is effectively applicable to other shapes and so
on, and is capable of providing the same operations and effects as
those of the above-described embodiment. Concretely, although an
example in which the molded product 100 is an audio volume knob was
described in the examples, the present invention is particularly
effectively applicable to a part being a molded product such as,
for instance, a temperature control knob in a vehicle interior, in
which a plate thickness of a side wall is hard to secure.
[0057] Further, an example in which the design surface 100a of the
molded product 100 is an outer surface was explained in the present
embodiment, but, the present invention is also effectively
applicable to a molded product in which both surfaces of a side
wall correspond to the design surfaces 100a. For example, when each
of clearances from the provisional rib portion 17 to the both
surfaces of the side wall cannot be set to 1 mm or more, by forming
all the corner portions of the connecting portion 17a between the
provisional rib portion 17 and the cavity 14 in a curved shape and
setting that R.gtoreq.0.5, it is possible to prevent the generation
of weld lines on the design surfaces of the side wall.
[0058] Further, explanation was made on an example in which the
arc-shaped corner portions (R portions 17b) are provided on a part
on the design surface 100a side as a curved shape of the connecting
portion 17a of the provisional rib portion 17. As the curved shape,
not only the one formed by the arc-shaped corner portions but also
an elliptical shape or a circular shape and the like can be
selected, for instance. Specifically, as shown in FIG. 6A or 6B,
all of the connecting portion 17a on the design surface 100a side
is formed in a semi-elliptical shape or semi-circular shape.
Further, the connecting portion 17a may also be formed in a
circular shape, as shown in FIG. 6C.
[0059] Further, although the submarine gate was employed in the
present embodiment, it is also possible to employ a so-called nose
gate from which molten resin is injected into the provisional rib
portion 17.
[0060] According to the present invention, the quality of outer
appearance of the injection-molded product can be improved with no
restriction on the molding material, and thus it is possible to
provide various types of injection-molded products with high
commercial value.
[0061] The present embodiments are to be considered in all respects
as illustrative and no restrictive, and all changes which come
within the meaning and range of equivalency of the claims are
therefore intended to be embraced therein. The invention may be
embodied in other specific forms without departing from the spirit
or essential characteristics thereof.
* * * * *